I have had to alter my dog walk to avoid these blighters. I know after a certain time they bury themselves ready to emerge in the summer, but, despite scouring the internet, ( and asking the natural History Museum who haven't replied. ) I can't find out how long it takes for them to get to this stage and disappear. I saw them for the first time 2 weeks ago, and would like to be able to work out when I can resume my proper walk without risk to the dogs..Any ideas? x

I'm not an entomologist but I suspect that you can't get an accurate timescale. In winter they spend the day in their nests and feed overnight. They tend to drop from their over-winter nests in late March/early April. They then search out a suitable place to pupate with soft soil where they can burrow into the ground. Given that different nests may drop at different times and that they can, in principle, process for up to one week they might be around for some time yet.

Thanks Warwick, that's really interesting, didn't occur to me that the nests would drop at different times, so really the answer is "How long is a piece of string?" .Last year they appeared earlier ,(end of Feb, but it was exceptionally warm), we avoided the area till May, so suspect will have to do the same. Sigh.

I am not sure exactly what acts as a signal to trigger them to drop from the nests. I am pretty sure it is weather dependent but whether it is something simple, like reaching a minimum temperature, or whether they sense a range of parameters I am not sure. I know that ant swarming is highly temperature critical and sometimes they will start to exit from the nest as flying ants and then retreat back in.

While the nests tend to be built where they will catch the most sun in winter it is not hard to imagine that each nest would reach some critical temperature on different days depending on their exact location. If you drive around on a motorbike at this time of year you certainly notice that there are warm and cold pockets of air.

Also the temperature doesn't steadily increase from day to day. You might get a warm day followed by several colder days. This could also mean that one nest, perhaps in a particularly favourable location, reached its critical temperature one day while another nest in a slightly less favourable location didn't. It might then be many days before the temperature overall got back up to the same level or slightly higher to allow the second nest to drop.

There's a Wikipedia article on them with some photos. Basically the processions that you see at this time of year is the final stage of the caterpillar phase before they pupate and then become a moth. The hairs they are covered with get more dangerous at each stage of the caterpillar phase and by this last stage they can even fire them at a nearby danger. They are very fine and barbed so they work their way into the skin where they inject a protein that irritates the skin and can cause severe allergic reactions in people and animals. If you put "dogs processionary caterpillars" into Google you'll find lots of articles and more images.

Don't touch them or get too close to them and watch out walking under trees that have the nests in them. They literally drop from the nests.

That was a really informative post Warwick , Thank You. I had read the article that you shared Jeff, and Wikipedia, that's why I give the area a wide berth. But none of them seemed to say how long before it was safe to go back after they had buried themselves ready for their next stage.